Originally Posted by
mark beiser
On the model and serial number sticker there is a date code. 3 digits with a circle around them.
If I remember correctly, the first digit is the final digit of the year, and the 2nd and 3rd digits are either the week or month of manufacture.
I'm not 100% certain on that, but my 3 Testo DRSAs have date codes of 504, 708, and 003, which corresponds with what I know the year of manufacture is of each one. 2005 for the 1st gen 523(still works flawlessly), 2007 for the 2nd gen 523(never worked for more than a couple of weeks at a time), and 2010 for the 550(repaired once, but otherwise has given good service).